The Pentagon building, headquarters of the United States Department of Defense. (AP Photo)

After concerns were raised earlier this year, the Pentagon has banned military troops and other workers at sensitive sites from using fitness trackers and other applications that can reveal the user's location.

In a memo obtained by The Associated Press, the Pentagon says that apps using a device's GPS function represent a risk to military activities and personnel.

"The rapidly evolving market of devices, applications, and services with geolocation capabilities presents a significant risk to Department of Defense (DoD) personnel both on and off duty, and to our military operations globally," it reads.

While devices such as smartwatches, tablets, cell phones or fitness trackers aren't themselves banned under the order, individual military leaders will be able to rule on whether local staff can use GPS, depending on the specific level of security threat. The rule will always apply in 'operational areas' and will cover government-issued devices as well as workers' own.

The move follows the discovery earlier this year by Nathan Ruser, a student studying international security at the Australian National University, that the fitness app Strava was revealing sensitive information through its publicly-available activity map.

For nearly two years, the app was displaying the movements of users in locations such as US bases in Afghanistan and Syria, a French military base in Niger and even Area 51.

Another researcher, Paul Dietrich, claimed he was even able to sue data scraped from the activity map to track one individual soldier from country to country.

Since then, there have been claims that other apps were similarly revealing: Polar Flow, for example, which was recently claimed by citizen journalist website Bellingcat to be revealing even more information than Strava.

There are a huge number of apps that can potentially reveal a user's location - everything from shopping apps to dating sites. According to the memo, staff will receive training to help them understand security risk, but the new regime is unlikely to be totally effective.

In the short term, that may not matter too much. It's groups of people using the same app in the same area that's the real give-away of troop movements; the odd jogger or lonely heart here or there won't be giving away too much information. However, in the longer term, the military may need a rather stricter regime than the new memo implies.

I've been writing about technology for most of my adult life, focusing mainly on legal and regulatory issues. I write for a wide range of publications: credits include the Times, Daily Telegraph and Financial Times newspapers, as well as BBC radio and numerous technology ti...